The present invention relates to a cleaning apparatus for a rotatable member used in an electrophotographic image forming apparatus.
In a known electrophotographic image forming apparatus, a photosensitive drum (an electrostatic latent bearing members) is rotated while a charging apparatus is used to apply a uniform electrostatic charge to the surface of the photosensitive drum, and a light beam is used to scan the surface of the photosensitive drum, thereby forming an electrostatic latent image on the photosensitive drum. A developer is applied to the electrostatic latent image upon the photosensitive drum, thus forming a development image upon the photosensitive drum, the development image is transferred from the photosensitive drum to recording paper and the development image on the recording paper is fixed by heat and pressure.
Here, the charging apparatus may be, for example, one wherein the charge is applied by corona discharge, or one wherein a brush is provided in the charging apparatus and the charge is applied by contact with the brush. With the former corona-discharge type of charging apparatus, the charge is applied to the photosensitive drum in a non-contact manner. Therefore, it has an advantage in that the charge on the photosensitive drum surface is uniform. However, it also has a drawback in that it generates large amounts of ozone.
On the other hand, with the latter brush-contact type of charging apparatus, a brush to which a bias voltage is applied is brought into contact with the surface of the photosensitive drum, thus applying a charge to the photosensitive drum. Accordingly, this has an advantage in that virtually no ozone is generated.
However, with the brush-contact type of charging apparatus, there is a drawback in that residual developer on the photosensitive drum or other fouling material may adhere to the brush, thus fouling the brush. This fouling of the brush could cause uneven charging or damage to the photosensitive drum, thus leading to degraded image quality.
More specifically, the developer on the photosensitive drum cannot be transferred onto recording paper at 100% transfer efficiency, resulting in residual developer on the photosensitive drum. This residual developer can be removed by bringing a cleaning rubber blade or the like in contact with (pressing) the surface of the photosensitive drum with a sufficient pressure. However, increasing the pressing strength of the rubber blade would scrape the photosensitive layer of the photosensitive drum, and therefore, the pressing strength of this rubber blade cannot be sufficiently strong. Accordingly, those components of the residual developer that have a small particle size, or those components of the residual developer that can form a strong electrostatic bond with the photosensitive drum cannot be removed, and the components of the residual developer on the photosensitive drum that have not been removed are absorbed electrostatically and caused to adhere to the brush of the charging apparatus.
For this reason, the brush-contact type of charging apparatuses are often provided with a cleaning mechanism for removing developer or the like adhering to the brush.
For example, in JP 2000-187373A (hereinafter referred to as “Patent Document 1”), the photosensitive drum and the rotatable member are rotated in directions opposite each other so that the charge is applied to the photosensitive drum while their outer circumferences are moving in the same direction in their areas of contact. Furthermore, the brush cleaner is rotated while the flocking of the rotatable member are pressed against the brush cleaner to remove fouling material from the rotatable member.
However, in Patent Document 1, although developer adhering to the flocking of the rotatable member is removed by the brush cleaner, there is no description on the removal of the developer adhering to the brush cleaner. Therefore, when the amount of the developer adhering to the brush cleaner increases, there is the possibility that the developer adhering to the brush cleaner may be reversely transferred to the rotatable member. Therefore, it cannot be said that the developer adhering to the flocking of the rotatable member is removed reliably.
In addition, another method for removing developer or the like adhering to the brush is to electrically remove residual developer from the brush. However, with this method, the electric field for removing the residual developer has a polarity opposite the polarity of charge of the photosensitive drum, producing an adverse effect on the charging characteristics of the photosensitive drum.
Moreover, such problems with rotatable members occur also with discharge brushes used to make contact with and discharge a photosensitive drum or the like, and cleaning brushes used to make contact with and clean a photosensitive drum or the like, causing uneven discharging and cleaning. That is to say, developer or other fouling material adheres to the rotatable member, resulting in unevenness in the characteristics of the rotatable member.
The present invention has been devised in consideration of these issues, and an object thereof is to provide a cleaning apparatus for a rotatable member by which it is possible to remove developer or other fouling material adhering to the rotatable member reliably and to prevent the disorder of the rotatable member.